Anisotropic high temperature thermal insulation flame retardant polyimide foam and its preparation method and use

Abstract

The application provides an anisotropic high-temperature heat-insulating flame-retardant polyimide foam and a preparation method and application thereof, and belongs to the field of advanced functional materials. The polyimide foam is obtained by sequentially subjecting copolyester ammonium salt precursor powder to microwave-assisted foaming, preliminary solidification and thermal imidization; the copolyester ammonium salt precursor powder is prepared from dianhydride and diamine; and the diamine is composed of 4,4'-diamino diphenyl ether and 4,4'-diamino diphenyl sulfone. The lightweight polyimide foam has good flexibility, excellent high-temperature heat-insulating performance, flame-retardant performance and outstanding radiation resistance. The polyimide foam has excellent comprehensive performance and can be used for heat protection and long-term service in extreme environments such as space exploration, high-speed aircraft, ships and nuclear reactors, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of advanced functional materials, specifically relating to an anisotropic high-temperature heat-insulating and flame-retardant polyimide foam, its preparation method, and its uses. Background Technology

[0002] Due to the presence of a three-dimensional matrix framework and air, polymer foams possess characteristics such as light weight, cushioning and shock absorption, and excellent thermal insulation properties. Currently, the most commonly used porous foams include polyethylene foam, melamine foam, polystyrene foam, and polyurethane foam. However, the application of these foams in industrial fields is limited because they cannot maintain their original properties under extreme cold / heat conditions, and their poor thermal stability and flammability are also factors. Furthermore, the aerospace, medical, and nuclear industries are experiencing a growing demand for lightweight, high-temperature resistant, flame-retardant, and radiation-resistant foams.

[0003] Aromatic polyimide foam (PIF) combines the advantages of polyimide resin and porous foam, and is a type of high-performance polymer foam containing aromatic benzene rings and imide rings in its molecular chain backbone. Therefore, polyimide foam possesses excellent mechanical properties, chemical and radiation resistance, high / low temperature resistance, flame retardancy, and thermal insulation properties. Furthermore, its wide range of applications in space exploration, marine transportation, nuclear power plants, and other fields has attracted widespread attention from industry and academia. The literature (Cai, R.; You, Y.; Wu, P.; Liu, Q.; Zhu, Y.; Zhang, S., Preparation of Open-Cell Rigid Polyimide Foam via Nonaqueous High Internal Phase Emulsion-Templating Technique. ACS Appl Polym Mater 2023, 5(10), 7795-7804, DOI: 10.1021 / acsapm.3c00994.) utilizes pyromellitic dianhydride and 4,4'-diaminodiphenylmethane to prepare rigid open-cell polyimide foam with excellent mechanical strength, thermal stability, and thermal insulation properties via emulsion-template technology. The density of the prepared polyimide foam is 56 kg / m³. 3It features a highly open-cell structure (100% open-cell ratio), a compressive strength of 0.2 MPa, and an initial thermal decomposition temperature of 528℃ under nitrogen atmosphere. Furthermore, the prepared polyimide foam exhibits excellent thermal insulation properties, with a thermal conductivity of 0.0389 W / (m·K) at 30℃ and 0.0449 W / (m·K) at 200℃. The literature (Yun, S.; Sheng, X.; Wang, S.; Miao, X.; Shi, X.; Zhao, Y.; Qin, J.; Zhang, G., Preparation and Properties of High-Temperature-Resistant, Lightweight, Flexible Polyimide Foams with Different Diamine Structures. Polymers 2023, 15(12), 2609, DOI: 10.3390 / polym15122609.) used polyester ammonium salt precursor powder as the starting derivative and prepared a series of foams with densities of 15-20 kg / m³ by stepwise heating foaming. 3 The prepared polyimide foam exhibits a glass transition temperature range of 270-340℃, a thermal conductivity of 0.046-0.053 W / (m·K) at 20℃ and 0.078-0.089 W / (m·K) at 200℃, and a limiting oxygen index ranging from 40.1-42.8%. However, the polyimide foam prepared in the above literature is insufficient for long-term service under extreme conditions (such as space, deep sea, and nuclear reactors), necessitating the development of polyimide foam materials with superior performance.

[0004] Copolymerization strategies can effectively introduce functional groups and rigid structures into the molecular chain backbone, thereby significantly improving the target properties of polyimide foams. The literature (Li,D.; Ke,Z.; Xu,K.; Dai,F.; Wang,M.; Chen,C.; Qian,G.; Yu,Y., Mechanically strong polyimide aerogels containing benzimidazole groups with excellent flame-retardant, thermal insulation and high service temperature. Chem Eng J 2023,461,141722,DOI:10.1016 / j.cej.2023.141722.) introduces 5-amino-2-(4-aminophenyl)benzimidazole into the 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride and 4,4′-diaminodiphenyl ether backbones, and prepares sol-gels using supercritical CO2 drying to produce foams with densities ranging from 117.5 to 230.9 kg / m³. 3 Polyimide aerogels were prepared. The results showed that the addition of benzimidazole heterocycles improved the intermolecular interactions, microstructure, and mechanical properties of the prepared polyimide aerogels. The literature (Sheng, X.; Yun, S.; Wang, S.; Gao, Y.; Zuo, X.; Miao, X.; Shi, X.; Qin, J.; Ma, Z.; Zhang, G., Highly heat-resistant and mechanically strong co-crosslinked polyimide / bismaleimide rigid foams with superior thermalinsulation and flame resistance. Mater Today Phys 2023, 36, 101154, DOI: 10.1016 / j.mtphys.2023.101154.) constructs a high-density polyimide / bismaleimide co-crosslinked network by copolymerizing norbornene-terminated polyimide oligomers with 4,4′-bismaleimide diphenylmethane, thereby incorporating the maleimide structure into the polyimide molecular chain. The introduction of high-rigidity monomers and the construction of a polyimide / bismaleimide co-crosslinking network endow rigid foams with smaller pore sizes and excellent thermal and mechanical properties. Thus, introducing functional groups and rigid structures into the molecular chain not only helps improve intermolecular interactions and microstructure, but also endows polyimide foams with superior properties, such as enhanced mechanical properties and excellent thermal insulation and flame retardant properties.

[0005] Therefore, developing a lightweight, high-mechanical-performance, heat-insulating, and flame-retardant material suitable for low-temperature / high-temperature applications has become both imperative and challenging. Summary of the Invention

[0006] The purpose of this invention is to provide an anisotropic high-temperature heat-insulating and flame-retardant polyimide foam, its preparation method, and its applications.

[0007] This invention provides an anisotropic high-temperature heat-insulating and flame-retardant polyimide foam, which is obtained by sequentially passing copolyester ammonium salt precursor powder through microwave-assisted foaming, preliminary curing, and thermal imidization.

[0008] The copolyester ammonium salt precursor powder is prepared from dianhydride and diamine as raw materials; the diamine is composed of 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl sulfone.

[0009] Furthermore, the molar ratio of the dianhydride to the diamine is (1-100):(1-100);

[0010] Preferably, the molar ratio of the dianhydride to the diamine is 1:1.

[0011] Further, the dianhydride is selected from one or more of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4'-biphenyl sulfone tetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, bisphenol A dianhydride, or hexafluorodianhydride;

[0012] Preferably, the dianhydride is selected from 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

[0013] Furthermore, the molar ratio of the 4,4'-diaminodiphenyl ether and the 4,4'-diaminodiphenyl sulfone is 1:1 to 9:1;

[0014] Preferably, the molar ratio of 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl sulfone is 7:3 or 5:5.

[0015] Furthermore, the solvent content in the copolyester ammonium salt precursor powder is 7-13%;

[0016] Preferably, the diameter of the copolyester ammonium salt precursor powder is 100-300 μm.

[0017] Furthermore, the preparation method of the copolyester ammonium salt precursor powder includes the following steps:

[0018] (1) Add a low-boiling-point solvent and a ring-opening catalyst to dianhydride and react to obtain a reaction solution;

[0019] (2) Add diamine, imidization catalyst and surfactant to the reaction solution, then add deionized water and reflux and stir to obtain copolyester ammonium salt precursor solution;

[0020] (3) Dry the copolyester ammonium salt precursor solution, grind and sieve it to obtain copolyester ammonium salt precursor powder.

[0021] Furthermore,

[0022] In step (1), the reaction is carried out in an inert environment, the reaction temperature is 50-100℃, and the reaction time is 1-10 hours.

[0023] And / or, in step (1), the mass of the ring-opening catalyst is 0.1 to 5% of the total mass of the dianhydride and diamine;

[0024] And / or, in step (2), the mass of the imidization catalyst is 0.1 to 5% of the total mass of the dianhydride and diamine;

[0025] And / or, in step (2), the mass of the surfactant is 0.5 to 5% of the total mass of the dianhydride and diamine;

[0026] And / or, in step (2), the temperature of the reaction is 50 to 100°C and the reaction time is 1 to 10 hours;

[0027] Preferably,

[0028] In step (1), the ring-opening catalyst is 2-methylimidazole;

[0029] And / or, in step (2), the imidization catalyst is isoquinoline;

[0030] And / or, in step (2), the surfactant is silicone oil DC-193.

[0031] Furthermore, the microwave-assisted foaming is first pre-foamed at 100-1000W microwave for 1-10 minutes, and then rapidly foamed at 500-2000W microwave for 1-20 minutes.

[0032] And / or, the initial curing is performed by microwave curing at 1000–3000W for 1–30 minutes;

[0033] And / or, the thermal imidization is performed at 250–350°C for 1–5 hours;

[0034] Preferably,

[0035] The microwave-assisted foaming process first involves pre-foaming at 560W microwave for 5-10 minutes, followed by rapid foaming at 700W microwave for 10-20 minutes.

[0036] And / or, the initial curing is performed by microwave curing at 1050W for 10–30 min;

[0037] And / or, the thermal imidization is performed at 280–300°C for 2–3 hours.

[0038] The present invention also provides a method for preparing the aforementioned polyimide foam, which includes the following steps:

[0039] (1) Add a low-boiling-point solvent and a ring-opening catalyst to dianhydride and react to obtain a reaction solution;

[0040] (2) Add diamine, imidization catalyst and surfactant to the reaction solution, then add deionized water and reflux and stir to obtain copolyester ammonium salt precursor solution;

[0041] (3) Dry the copolyester ammonium salt precursor solution, grind and sieve it to obtain copolyester ammonium salt precursor powder;

[0042] (4) The copolyester ammonium salt precursor powder is successively subjected to microwave-assisted foaming, preliminary curing and thermal imidization to obtain polyimide foam.

[0043] The present invention also provides the use of the aforementioned polyimide foam in the preparation of lightweight, flexible, high-temperature heat-insulating and flame-retardant materials for use in the fields of aerospace, transportation, electronics and electrical, nuclear power equipment, and new energy.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] This invention provides a method for synthesizing copolyester ammonium salt precursor powder via a copolymerization strategy, and further preparing anisotropic porous polyimide foam through microwave-assisted foaming, preliminary curing, and high-temperature thermal imidization. This lightweight polyimide foam exhibits good mechanical flexibility, excellent high-temperature thermal insulation and flame retardant properties, and outstanding radiation resistance. Due to its superior overall performance, this polyimide foam can achieve long-term service in extreme applications such as space exploration, deep-sea exploration, and nuclear reactors, providing inspiration for high-temperature thermal protection, infrared stealth, and flame retardant applications in extreme environments. Furthermore, the polyimide foam production method of this invention is simple, allows for large-scale production, and has promising application prospects.

[0046] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions, or alterations can be made without departing from the basic technical concept of the present invention.

[0047] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0048] Figure 1 The images shown are optical images of the polyimide foam of the present invention, as well as SEM images of the pores, walls, and film in the horizontal and vertical directions: a1-a5 are, in order, optical images, horizontal pore SEM images, vertical pore SEM images, pore wall SEM images, and pore film SEM images of the polyimide foam prepared in Comparative Example 1; b1-b5 are, in order, optical images, horizontal pore SEM images, vertical pore SEM images, pore wall SEM images, and pore film SEM images of the polyimide foam prepared in Example 3.

[0049] Figure 2 The mechanical properties of the polyimide foam of this invention are as follows: a1-a2 are the compression curves and compressive strengths in the vertical direction, respectively; b1-b2 are the compression curves and compressive strengths in the horizontal direction, respectively; c1-c2 are the tensile curves and tensile strengths in the horizontal direction, respectively.

[0050] Figure 3 The results of the high-temperature thermal insulation and flame retardant properties of the polyimide foam of the present invention are as follows: a) Thermal conductivity of the foam sample in the vertical direction at 25°C; b) Thermal conductivity of the foam sample in the horizontal direction at 25°C; c) Thermal conductivity of the polyimide foam prepared in Example 3 in the vertical direction at different temperatures; d) Limiting oxygen index value of the polyimide foam.

[0051] Figure 4 The images shown are of the polyimide foam of the present invention: a is a combustion image of the polyimide foam prepared in Comparative Example 1; b is a combustion image of the polyimide foam prepared in Example 5. Detailed Implementation

[0052] The raw materials and equipment used in the specific embodiments of the present invention are all known products, obtained by purchasing commercially available products.

[0053] Example 1: Preparation of the polyimide foam of the present invention

[0054] (1) Preparation of copolyester ammonium salt precursor powder

[0055] Copolyester ammonium salt precursor powder was prepared using 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) as the dianhydride monomer and 4,4'-diaminodiphenyl ether (ODA) and 4,4'-diaminodiphenyl sulfone (DDS) as diamine monomers. First, 64.45 g (0.2 mol) of BTDA, 54.01 mL of anhydrous methanol, 81.22 mL of tetrahydrofuran, and 0.30 g of 2-methylimidazole were heated under nitrogen protection and refluxed at 65 °C for 1 hour to obtain a clear and transparent solution of aromatic diacid diester. Then, the diamine monomer was prepared according to a copolymerization ratio of ODA:DDS = 9:1 (molar ratio). Specifically, 36.04 g (0.18 mol) of ODA and 4.97 g (0.02 mol) of DDS were added to the above clear and transparent solution, along with 0.24 mL of isoquinoline and 0.50 mL of silicone oil DC-193. The mixture was heated under reflux at 70°C for 2 hours, cooled to room temperature, and then 3.32 mL of deionized water was added. The mixture was stirred and refluxed for 1 hour to obtain a copolyester ammonium salt precursor solution. The copolyester ammonium salt precursor solution was dried to obtain a brownish-brown blocky solid with a solvent content of 7–13%. After grinding and sieving, a copolyester ammonium salt precursor powder of 100–300 μm was obtained.

[0056] (2) Preparation of polyimide foam (PIF)

[0057] Add the copolyester ammonium salt precursor powder to a mold, seal the mold, and place it in a microwave reactor. Pre-foam at 560W on low power for 5 minutes, then rapidly foam at 700W on medium power for 10 minutes. Finally, pre-cure at 1050W on high power for 10 minutes. Finally, heat-imide treatment at 280℃ for 2 hours yields polyimide foam, named PIF according to the copolymerization ratio. B / O9-D1 .

[0058] Example 2: Preparation of the polyimide foam of the present invention

[0059] Except for the preparation of diamine monomers in Example 1(1) with a copolymerization ratio of ODA:DDS = 8:2 (molar ratio), i.e., 32.04 g (0.16 mol) ODA and 9.93 g (0.04 mol) DDS, the other operations were the same as in Example 1, and polyimide foam was obtained, named PIF. B / O8-D2 .

[0060] Example 3: Preparation of the polyimide foam of the present invention

[0061] Except for the preparation of diamine monomers in Example 1(1) with a copolymerization ratio of ODA:DDS = 7:3 (molar ratio), i.e., 28.03 g (0.14 mol) ODA and 14.90 g (0.06 mol) DDS, the other operations were the same as in Example 1, and polyimide foam was obtained, named PIF. B / O7-D3 .

[0062] Example 4: Preparation of the polyimide foam of the present invention

[0063] Except for the preparation of diamine monomers in Example 1(1) with a copolymerization ratio of ODA:DDS = 6:4 (molar ratio), i.e., 24.03 g (0.12 mol) ODA and 19.86 g (0.08 mol) DDS, the other operations were the same as in Example 1, and polyimide foam was obtained, named PIF. B / O6-D4 .

[0064] Example 5: Preparation of the polyimide foam of the present invention

[0065] Except for the preparation of diamine monomers in Example 1(1) with a copolymerization ratio of ODA:DDS = 5:5 (molar ratio), i.e., 20.02 g (0.1 mol) ODA and 24.83 g (0.1 mol) DDS, the other operations were the same as in Example 1, and polyimide foam was obtained, named PIF. B / O5-D5 .

[0066] Comparative Example 1: Preparation of the polyimide foam of the present invention

[0067] Except for the preparation of diamine monomers in Example 1(1) with a copolymerization ratio of ODA:DDS = 10:0 (molar ratio), i.e., 40.05 g (0.2 mol) ODA and 0 g (0 mol) DDS, the other operations were the same as in Example 1, and polyimide foam was obtained, named PIF. B / O10-D0 .

[0068] The following specific experimental examples demonstrate the beneficial effects of the present invention.

[0069] Experimental Example 1: Optical and Anisotropic Porous Structure of Polyimide Foam of the Present Invention

[0070] 1. Experimental Methods

[0071] The polyimide foams prepared in Examples 1-5 and Comparative Example 1 were used to observe optical images. Simultaneously, the SEM cell, cell wall, and cell membrane structures were observed in both the horizontal direction (i.e., perpendicular to the pore growth direction) and the vertical direction (i.e., parallel to the pore growth direction), and the pore size was measured using nanoscale testing software.

[0072] 2. Experimental Results

[0073] like Figure 1As shown, the polyimide foams exhibit a very uniform and good appearance. Due to the microwave-assisted directional foaming process, the foams exhibit an anisotropic porous structure. When viewed horizontally, they show a neatly arranged elliptical strip-shaped pore structure; while when viewed vertically, they show a regular three-dimensional porous near-spherical appearance.

[0074] As shown in Table 1, a statistical analysis was performed on the cells, walls, and membranes in the vertical direction of the foam. B / O10-D0 PIF B / O9-D1 PIF B / O8-D2 PIF B / O7-D3 PIF B / O6-D4 and PIF B / O5-D5 The average pore sizes are 342, 332, 293, 269, 283, and 295 μm, respectively, with corresponding bubble wall and bubble film thicknesses ranging from 3 to 10 μm and 600 to 800 nm, respectively. The anisotropic polyimide foam exhibits micron / nano multi-scale porous structure characteristics.

[0075] Table 1. Physical properties of the polyimide foam of the present invention

[0076]

[0077] Test Example 2: Mechanical Flexibility of the Polyimide Foam of the Present Invention

[0078] 1. Experimental Methods

[0079] Polyimide foams prepared in Examples 1-5 and Comparative Example 1 were used. The apparent density of the foams was calculated according to GB / T 6343-2009, and the open-cell ratio was evaluated using an automatic true density meter according to GB / T 10799-2008. The mechanical properties of the foam samples in the vertical and horizontal directions, including compressive and tensile properties, were evaluated using a general-purpose mechanical testing instrument. The compression rate was 2 mm / min, and the tensile rate was 1 mm / min. Each sample was tested three times repeatedly, and the average value was reported. In this test, the horizontal direction is perpendicular to the pore growth direction, and the vertical direction is parallel to the pore growth direction.

[0080] 2. Experimental Results

[0081] As shown in Table 1, polyimide foams with different copolymerization ratios exhibit lightweight properties (density 17-24 kg / m³). 3 It possesses a high open-cell ratio (93-97%) and excellent mechanical flexibility in both directions, with a compression recovery rate as high as 97-99%. The mechanical properties of the foam were evaluated through compression and tensile tests. Figure 2As shown, the compressive stress-strain curves and compressive strength values ​​in the vertical and horizontal directions indicate that the foam possesses anisotropic mechanical properties. In the vertical direction, the curves exhibit three characteristic deformation regions: a linear elastic region, a stress plateau region, and a densification region. In the horizontal direction, the curves show two characteristic deformation regions: a linear elastic region and a stress growth region. These results indicate that the polyimide foam has good mechanical flexibility. The compressive strength in the vertical direction is approximately 1-3 times that in the horizontal direction, with the maximum compressive strengths in the vertical and horizontal directions being 61.77 kPa and 38.82 kPa, respectively. The tensile strength shows the same trend as the compressive strength, with a maximum tensile strength of 103.19 kPa. The trends in compressive and tensile strength are mainly related to the foam's density, molecular structure rigidity, and pore structure. In summary, the polyimide foam with anisotropic porous structure prepared in this invention exhibits good mechanical properties and mechanical flexibility.

[0082] Test Example 3: Thermal stability of the polyimide foam of the present invention

[0083] 1. Experimental Methods

[0084] The polyimide foams prepared in Examples 1-5 and Comparative Example 1 were used to evaluate the thermal stability of the foams by heating them from 35°C to 800°C at a rate of 10°C / min under air and nitrogen atmospheres using a thermogravimetric analyzer. The heat resistance of the foams was evaluated by differential scanning calorimetry (DSC 3500Sirius) under nitrogen atmosphere.

[0085] 2. Experimental Results

[0086] As shown in Table 2, the initial thermal decomposition temperature (T) of the foam under a nitrogen atmosphere is... 5％ The residual weight (R) occurs between 546-552℃ and at 800℃. 800 The thermal stability of the foam is 53%-56%, exhibiting good thermal stability. However, in an air atmosphere, oxygen accelerates the thermal degradation of molecular chain segments, leading to a decrease in the Tg of the foam. 5％ (521-534℃) and R 800 (1.5-2.4%) all decreased. DSC results showed that the glass transition temperature (T) of the foam decreased. g The temperature ranges from 283 to 312℃, and the heat resistance of polyimide foams with different copolymerization ratios increases with the increase of molecular chain rigidity. These results demonstrate that the polyimide foam prepared in this invention possesses excellent thermal stability and heat resistance, thus having significant application value under high-temperature conditions.

[0087] Table 2. Thermal stability of the polyimide foam of the present invention

[0088]

[0089]

[0090] Test Example 4: High-Temperature Thermal Insulation Performance of the Polyimide Foam of the Present Invention

[0091] 1. Experimental Methods

[0092] The polyimide foams prepared in Examples 1-5 and Comparative Example 1 were used, and their thermal conductivity at 25, 100, 200, and 300 °C was evaluated using a thermal constant analyzer. To qualitatively evaluate the insulation behavior of the foams, the temperature change of the top surface of the foam samples placed on a 200 °C preheating stage was recorded using an infrared thermal imager. In this experimental example, the horizontal direction is perpendicular to the pore growth direction, and the vertical direction is parallel to the pore growth direction.

[0093] 2. Experimental Results

[0094] like Figure 3 As shown in a-3b, polyimide foams with different copolymerization ratios exhibit low thermal conductivity at 25°C, ranging from 0.0276 to 0.0307 W / (m·K) vertically and from 0.0276 to 0.0298 W / (m·K) horizontally, close to that of air (0.0262 W / (m·K)). Furthermore, due to the high thermal stability and heat resistance of the polyimide foam of this invention, it can be used as a thermal insulation material under high-temperature conditions. Based on this, PIF was selected. B / O7-D3 Vertical thermal conductivity was tested at different temperatures, and the results showed that ( Figure 3 c) As the temperature increased from 25°C to 300°C, the thermal conductivity increased from 0.0276 W / (m·K) to 0.0517 W / (m·K). Furthermore, the thermal conductivity of the polyimide foam of this invention is slightly lower in the horizontal direction than in the vertical direction. Infrared thermal imaging technology was used to further evaluate the thermal insulation performance and infrared stealth performance in different directions. As shown in Table 3, after 30 minutes on a 200°C preheating platform, the top surface temperature of the Example 3 sample in the horizontal direction (64.2°C) was lower than that in the vertical direction (79.6°C). This is mainly because heat in the vertical direction is transferred along the neatly arranged elliptical strip-shaped pore structure, while heat transfer in the horizontal direction is affected by the increased heat dissipation path and the presence of air in the pores. In summary, the polyimide foam of this invention has excellent high-temperature thermal insulation performance and can achieve a wide range of applications.

[0095] Table 3. Thermal insulation performance of the polyimide foam of the present invention

[0096]

[0097] Test Example 5: Flame retardant properties of the polyimide foam of the present invention

[0098] 1. Experimental Methods

[0099] The polyimide foams prepared in Examples 3, 5 and Comparative Example 1 were used. The limiting oxygen index (LOI) of the polyimide foams was determined according to GB / T 2406.2-2009. The flame retardant properties of the polyimide foams were evaluated by an alcohol lamp burning test.

[0100] 2. Experimental Results

[0101] like Figure 3 As shown in d, with the increase of DDS content, the LOI value of the polyimide foam sample shows a significant upward trend, among which PIF B / O5-D5 The LOI value reached a maximum of 58.8%, demonstrating excellent flame retardant properties. Notably, all polyimide foam samples exhibited self-extinguishing properties upon removal from the flame, with a burning time of less than 180 seconds. Introducing phenyl sulfone groups (from DDS) into the polyimide foam molecular structure via a copolymerization strategy improved the flame retardancy of the polyimide foam, attributed to its high thermal stability and the synergistic mechanism of gas-phase and condensed-phase flame retardancy.

[0102] like Figure 4 As shown, the flame-retardant properties of the polyimide foam of this invention were directly evaluated using an alcohol lamp burning test. Throughout the combustion process, the bottom of the polyimide foam strip remained in contact with the flame. The bottom of the foam sample charred and turned black, but the upper structure remained stable without significant damage, demonstrating excellent heat transfer insulation and flame-retardant properties. It is worth noting that PIF... B / O5-D5 The length of the spline after combustion is higher than that of the PIF. B / O10-D0 The presence of fewer carbonized regions in the sample indicates that the introduction of DDS through a copolymerization strategy improves the flame-retardant properties of the polyimide foam of this invention.

[0103] Test Example 6: Radiation resistance of the polyimide foam of the present invention

[0104] 1. Experimental Methods

[0105] The polyimide foams prepared in Examples 3, 5 and Comparative Example 1 were used... 60 Co was used as a gamma-ray radiation source (1.2 MeV) to conduct radiation tests on foam samples, with a total radiation dose of 1.15 × 10⁻⁶. 5 The thermal stability of irradiated polyimide foam samples was evaluated using a thermogravimetric analyzer under a nitrogen atmosphere, heating from 35°C to 800°C at a rate of 10°C / min. The compressibility of the irradiated polyimide foam samples in the vertical direction (i.e., parallel to the pore growth direction) was evaluated using a general mechanical testing instrument at a compression rate of 2 mm / min. Each sample was tested three times, and the average value was reported.

[0106] 2. Experimental Results

[0107] The radiation resistance of the polyimide foam of this invention was evaluated by assessing the changes in optical morphology, molecular structure, microstructure, thermal stability, and mechanical properties before and after irradiation. After irradiation treatment, the optical morphology, molecular structure, and microstructure of the polyimide foam remained stable, which is crucial for maintaining its mechanical properties. Table 4 shows the initial thermal decomposition temperature, char residue at 800°C, and compressive strength of the polyimide foam samples before and after irradiation. The initial thermal decomposition temperature retention rate of the irradiated polyimide foam was higher than 98.8%, and the 10% compressive strength retention rate in the vertical direction was higher than 96.2%. Furthermore, the density of the irradiated polyimide foam remained unchanged (15-25 kg / m³). 3 Furthermore, it retains mechanical flexibility (compression recovery rate of 98%), which is related to the preservation of its porous structure. Therefore, the polyimide foam of this invention exhibits excellent radiation resistance and shows great application potential in the nuclear industry.

[0108] Table 4. Radiation resistance properties of the polyimide foam of the present invention

[0109]

[0110] In summary, this invention provides a method for synthesizing copolyester ammonium salt precursor powder via a copolymerization strategy, and further preparing anisotropic porous polyimide foam through microwave-assisted foaming, preliminary curing, and high-temperature thermal imidization. This lightweight polyimide foam exhibits good mechanical flexibility, excellent high-temperature thermal insulation and flame retardant properties, and outstanding radiation resistance. Due to its superior comprehensive performance, this polyimide foam can achieve long-term service in extreme fields such as space exploration, deep-sea exploration, and nuclear reactors, and also provides inspiration for high-temperature thermal protection, infrared stealth, and flame retardant applications in extreme environments. Furthermore, the polyimide foam production method of this invention is simple, can achieve large-scale production, and has good application prospects.

Claims

1. An anisotropic high-temperature insulating and flame-retardant polyimide foam, characterized in that: It is obtained by sequentially passing copolyester ammonium salt precursor powder through microwave-assisted foaming, preliminary curing, and thermal imidization. The preparation method of the copolyester ammonium salt precursor powder includes the following steps: (1) Add a low-boiling-point solvent and a ring-opening catalyst to the dianhydride and react to obtain a reaction solution; (2) Add diamine, imidization catalyst and surfactant to the reaction solution, then add deionized water and stir under reflux to obtain a copolyester ammonium salt precursor solution; (3) Dry the copolyester ammonium salt precursor solution, grind and sieve it to obtain copolyester ammonium salt precursor powder; The molar ratio of the dianhydride to the diamine is 1:1; the dianhydride is selected from 3,3',4,4'-benzophenone tetracarboxylic dianhydride; the diamine is composed of 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl sulfone, and the molar ratio of 4,4'-diaminodiphenyl ether to 4,4'-diaminodiphenyl sulfone is 5:

5.

2. The polyimide foam according to claim 1, characterized in that: The solvent content in the copolyester ammonium salt precursor powder is 7-13%.

3. The polyimide foam according to claim 2, characterized in that: The diameter of the copolyester ammonium salt precursor powder is 100~300μm.

4. The polyimide foam according to claim 1, characterized in that: In step (1), the reaction is carried out in an inert environment, the reaction temperature is 50~100℃, and the reaction time is 1~10 hours; And / or, in step (1), the mass of the ring-opening catalyst is 0.1-5% of the total mass of the dianhydride and diamine; And / or, in step (2), the mass of the imidization catalyst is 0.1-5% of the total mass of the dianhydride and diamine; And / or, in step (2), the mass of the surfactant is 0.5-5% of the total mass of the dianhydride and diamine; And / or, in step (2), the temperature of the reaction is 50~100℃ and the reaction time is 1~10 hours.

5. The polyimide foam according to claim 4, characterized in that: In step (1), the ring-opening catalyst is 2-methylimidazole; And / or, in step (2), the imidization catalyst is isoquinoline; And / or, in step (2), the surfactant is silicone oil DC-193.

6. The polyimide foam according to claim 1, characterized in that: The microwave-assisted foaming process first involves pre-foaming at 100-1000W microwave for 1-10 minutes, followed by rapid foaming at 500-2000W microwave for 1-20 minutes. And / or, the initial curing is performed by microwave curing at 1000~3000W for 1~30 minutes; And / or, the thermal imidization is performed at 250~350°C for 1~5 hours.

7. The polyimide foam according to claim 1, characterized in that: The microwave-assisted foaming process first involves pre-foaming at 560W microwave for 5-10 minutes, followed by rapid foaming at 700W microwave for 10-20 minutes. And / or, the initial curing is performed by microwave curing at 1050W for 10-30 minutes; And / or, the thermal imidization is performed at 280~300°C for 2~3 hours.

8. A method for preparing the polyimide foam according to any one of claims 1 to 7, characterized in that: It includes the following steps: (1) Add a low-boiling-point solvent and a ring-opening catalyst to the dianhydride and react to obtain a reaction solution; (2) Add diamine, imidization catalyst and surfactant to the reaction solution, then add deionized water and stir under reflux to obtain a copolyester ammonium salt precursor solution; (3) Dry the copolyester ammonium salt precursor solution, grind and sieve it to obtain copolyester ammonium salt precursor powder; (4) The copolyester ammonium salt precursor powder is successively subjected to microwave-assisted foaming, preliminary curing and thermal imidization to obtain polyimide foam.

9. The use of the polyimide foam according to any one of claims 1 to 7 in the preparation of lightweight, flexible, high-temperature heat-insulating and flame-retardant materials for use in the fields of aerospace, transportation, electronics and electrical engineering, nuclear power equipment, and new energy.

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